The present invention relates to an inkjet head and an inkjet recording apparatus. More particularly, it relates to the inkjet head with low noise and high speed at recording operation due to driving an actuatorxe2x80x94ejecting inkxe2x80x94at a frequency not less than 20 kHz. The present invention also relates to the inkjet recording apparatus using this inkjet head.
An inkjet head of a conventional inkjet recording apparatus ejects ink by piezoelectric effect of a piezoelectric element. This kind of head comprises, in general, the following elements:
(a) a head body formed by a plurality of pressure chambers containing ink and a plurality of nozzles communicating through each chamber;
(b) a piezoelectric actuator for ejecting ink from the nozzle by deforming itself so that a capacity of each pressure chamber increases/decreases; and
(c) a control circuit for supplying a drive signal to the actuator.
When the actuator is driven, sound pressure occurs upon its deformation, and thus an operator hears a harsh driving noise of the actuator.
In particular, recently, an inkjet recording apparatus has been expected to produce a quality picture at high speed, and thus when a number of nozzles is increased in order to upgrade picture quality, numbers of piezoelectric actuators are prepared. Thus the operator hears louder driving noise. On the other hand, when a driving frequency of the piezoelectric actuator is increased in order to gain a recording speed, driving noise of a rather high frequency occurs. This noise sounds extremely harsh to the users.
When a dc motor with less noise is used as a driver for moving the head and recording medium in order to reduce the moving noise of the apparatus, the driving noise of the actuator sounds relatively louder, and it sounds harsher to the users.
Japanese patent application non-examined publication No. H05-238008 discloses a countermeasure against the problem discussed above, i.e., a piezoelectric actuator for ejecting ink is provided to a pressure chamber containing ink, and another piezoelectric actuator for a non-ejecting purpose is provided to a pressure chamber which does not contain ink. Thus the inkjet head as a whole is driven at 16 kHz, which is out of audible range, by driving these actuators alternately. In this case, however, the actuator for a non-ejecting purpose must be prepared only for obtaining a driving frequency of 16 kHz, and this actuator is not needed regularly.
In the inkjet head disclosed in the above publication, a number of vibrations of vibration system proper to each actuator differs from each other due to processing accuracy of, e.g., the pressure chambers and actuators. Therefore, when both the actuators are respectively driven, different sound pressures occur alternately, which sounds rather louder to the users in spite of the original purpose, i.e., lowering the noise.
The present invention addresses the problems discussed above, and aims to provide an inkjet head as well as an inkjet recording apparatus which can lower the noise and record at high speed. The inkjet head of the present invention comprises the following elements:
(a) at least one pressure chamber containing ink;
(b) a nozzle communicating through the pressure chamber;
(c) at least one piezoelectric actuator having a piezoelectric element and deforming itself by piezoelectric effect of the piezoelectric element so that the capacity of the pressure chamber increases or decreases; and
(d) a controller for driving the piezoelectric actuator at a frequency not less than 20 kHz and for controlling the ink in the pressure chamber to be ejected from the nozzle at a desired timing.
This structure allows the controller to drive the piezoelectric actuator at the frequency not less than 20 kHz, so that the driving noise of the actuator is out of audible range and the user hardly hear this noise. This structure differs from the inkjet head disclosed in the publication discussed previously and can drive the actuator with less driving noise without the actuator for the non-ejecting purpose. In this structure, since one actuator is driven at the frequency not less than 20 kHz, the same sound pressure occurs positively at not less than 20 kHz compared with a case where two types of actuators are alternately driven. As a result, driving noise becomes surely smaller.
The inkjet recording apparatus of the present invention comprises the following elements:
(a) the inkjet head discussed above; and
(b) a moving device for moving the head relative to a recording medium, and while the head is moved relative to the recording medium by the moving device, a nozzle ejects ink onto the recording medium to carry out the recording. This structure allows the apparatus to provide the same advantage as discussed above.
Another inkjet recording apparatus of the present invention comprises the following elements:
(a) at least one inkjet head including:
(a-1) at least one pressure chamber containing ink;
(a-2) at least one nozzle for communicating through the pressure chamber;
(a-3) at least one actuator for increasing the pressure of the pressure chamber; and
(a-4) a controller for driving the piezoelectric actuator at a frequency not less than 20 kHz and for controlling the ink in the pressure chamber to be ejected from the nozzle at a desired timing;
(b) a first dc motor for moving a carriage, to which the head is mounted, in a main scanning direction; and
(c) a second dc motor for moving a recording medium in a sub-scanning direction.
This structure allows the apparatus to reduce the operation noise by using the dc motors instead of stepping motors for moving the carriage and the recording medium. Further, because the driving noise of the head makes little sound, the apparatus as a whole can be expected to undergo substantially noiseless operation.